1. Field of the Invention
The present invention relates to a method of fabricating photodiode arrays. More specifically, the invention relates to a method of fabricating photodiode arrays with non-alloyed contacts and uniform responsivity by selectively etching a contact epilayer prior to passivation of the photodiode array.
2. Related Art
Low dark current photodiode arrays are extremely useful in the opto-electronic industry. Such arrays can be employed in applications including fiber-optic networking, spectral power monitoring, and spatial positioning sensors. Conventional methods of fabricating such arrays, however, suffer from significant shortcomings.
According to such conventional fabrication methods, diffusion processes are typically used to form diode (xe2x80x9cp-nxe2x80x9d) junctions by introducing a dopant into a semiconductor substrate by passing the dopant though a combined dielectric passivation and diffusion mask. Such masks also serve to passivate the semiconductor surface areas that intersect the p-n junctions. After diffusion, the surface areas are again covered with a new passivation layer that also serves as an antireflective (xe2x80x9cARxe2x80x9d) coating.
The process of removing initial passivation coatings after the dopant has been diffused, and re-passivating the semiconductor with dielectric coatings, increases dark current in the semiconductor, thereby significantly reducing efficiency. Further, the dielectric coatings often have non-uniform thicknesses, resulting in non-uniform dispersion of light reflected off of the semiconductor and causing interference and reduced efficiency when the semiconductor is used in spectral monitoring applications. Additionally, the initial passivation coatings are frequently applied to semiconductor surfaces that are not fresh; prior to initial passivation, the semiconductor surface is often given ample time to undergo microscopic reconstruction due to the exchange of surface matter with gases in the surrounding atmosphere. Even further, contacts placed on the semiconductor surface often are not optimally arranged, thus requiring the application of alloyed contacts to reduce electrical yield per contact area. Finally, when non-gaseous dopant sources are used in conventional diffusion processes, additional cleaning processes that damage the combined passivation/diffusion mask must be used, thereby making the surface difficult to re-passivate and ultimately degrading the quality of the resulting photodiode array.
These and other shortcomings of conventional photodiode array fabrication methodologies are solved by the present invention, described below in further detail.
It is an object of the present invention to provide a method of fabricating low dark current photodiode arrays.
It is a further object of the present invention to provide a method of fabricating low dark current photodiode arrays with non-alloyed contacts and uniform responsivity.
It is another object of the present invention to provide a method of fabricating low dark current photodiode arrays by selectively etching a contact epilayer prior to passivation of the semiconductor.
It is an additional object of the present invention to provide a semiconductor having passivation and AR coating thicknesses that are uniform throughout the entire surface area of the semiconductor.
It is a further object of the present invention to provide a method of fabricating low dark current photodiodes wherein the semiconductor surface is protected by an epitaxial layer prior to passivation.
It is an additional object of the present invention to provide a method of fabricating low dark current photodiodes having contact epilayers that provide low series resistance and contribute to high array resolution.
It is another object of the present invention to provide a photodiode array wherein, prior to passivation, the contact epilayer protects the semiconductor surface from non-gaseous dopant sources.
The present invention relates to a method for fabricating low dark current semiconductor photodiode arrays having non-alloyed contacts and uniform responsivity by selective etching of a contact epilayer prior to passivation of the semiconductor. A semiconductor having doped layers is first provided. A contact layer is deposited on the semiconductor, and a diffusion mask is deposited on the contact layer. Holes are opened in the diffusion mask, and dopant is diffused therethrough, into both the contact layer and the semiconductor. A new etch mask is deposited and etched. The contact layer is then selectively etched so that only islands remain where contacts are to be deposited. The semiconductor is passivated with a uniform single- or multi-layer coating, which may also serve as an anti-reflective (AR) coating. Metal contacts and bond pads are deposited, thereby formulating a complete, low dark current semiconductor photodiode array.
The method of the invention can be altered to allow for deposition of metal contacts prior to partial etch removal of the contact epilayer, thereby allowing the metal contacts to serve as an etch mask. If the contact metal is capable of being used as a bond pad metal, both the contact metal and the bond pad metal can be deposited in the same pass.